Re: [PATCH 2/2] mm: support poison recovery from copy_present_page()

[Miaohe Lin <linmiaohe@xxxxxxxxxx>]

On 2024/9/10 14:35, Kefeng Wang wrote:
> 
> 
> On 2024/9/10 10:19, Miaohe Lin wrote:
>> On 2024/9/6 10:42, Kefeng Wang wrote:
>>> Similar to other poison recovery, use copy_mc_user_highpage() to
>>> avoid potentially kernel panic during copy page in copy_present_page()
>>> from fork, once copy failed due to hwpoison in source page, we need
>>> to break out of copy in copy_pte_range() and release prealloc folio,
>>> so copy_mc_user_highpage() is moved ahead before set *prealloc to NULL.
>>>
>>> Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
>>> ---
>>>   mm/memory.c | 10 +++++++---
>>>   1 file changed, 7 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/mm/memory.c b/mm/memory.c
>>> index d310c073a1b3..6e7b78e49d1a 100644
>>> --- a/mm/memory.c
>>> +++ b/mm/memory.c
>>> @@ -926,8 +926,11 @@ copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma
>>>        * We have a prealloc page, all good!  Take it
>>>        * over and copy the page & arm it.
>>>        */
>>> +
>>> +    if (copy_mc_user_highpage(&new_folio->page, page, addr, src_vma))
>>> +        return -EHWPOISON;
>>> +
>>>       *prealloc = NULL;
>>> -    copy_user_highpage(&new_folio->page, page, addr, src_vma);
>>>       __folio_mark_uptodate(new_folio);
>>>       folio_add_new_anon_rmap(new_folio, dst_vma, addr, RMAP_EXCLUSIVE);
>>>       folio_add_lru_vma(new_folio, dst_vma);
>>> @@ -1166,8 +1169,9 @@ copy_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
>>>           /*
>>>            * If we need a pre-allocated page for this pte, drop the
>>>            * locks, allocate, and try again.
>>> +         * If copy failed due to hwpoison in source page, break out.
>>>            */
>>> -        if (unlikely(ret == -EAGAIN))
>>> +        if (unlikely(ret == -EAGAIN || ret == -EHWPOISON))
>>
>> Will it be better to put checking ret against -EHWPOISON in a new line? -EAGAIN case will enter the
>> loop again but -EHWPOISON case never does.
> 
> Maybe not a newline since we will recheck the ret in the below and return directly from copy_present_page().

Anyway, this patch looks good to me.

Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>

Thanks.
.